P1060: REAL-WORLD CLINICAL OUTCOMES AFTER 3 AND 6 MONTHS OF TREATMENT WITH FEDRATINIB FOLLOWING RUXOLITINIB FAILURE
Authors: J. Mascarenhas, A. T. Gerds, J. K. Kish, P. Abraham, A. Balanean, J. A. Nadal, D. Liassou, B. A. Feinberg, A. McBride, C. Harrison
Journal: HemaSphere (2022)

Background: Relief of symptoms and splenomegaly is an important treatment (Tx) goal for patients with myelofibrosis (MF). Fedratinib (FEDR) and ruxolitinib (RUX) are approved in the USA for Intermediate (Int)- or High-risk (HR) primary or secondary MF. Aims: To describe spleen size, and hematologic and MF-specific symptoms, during the first 6 months of FEDR therapy after prior Tx with RUX in US clinical practices. Methods: Adults with Int- or HR MF who initiated FEDR on or after August 16, 2019 (FEDR approval date) and with ≥90 days of follow-up were identified from community oncology practices. Eligible patients were those treated with RUX and then FEDR, who had spleen palpation at FEDR initiation, and who had completed ≥1 cycle of FEDR. Treating physicians completed electronic case report forms for the selected eligible patients, extracting patient characteristics, Tx pattern data, and clinical outcomes such as spleen size, MF-related symptoms per the Myelofibrosis Symptom Assessment Form version 4.0 (MFSAF v4.0), hemoglobin (Hb), and platelet and white blood cell (WBC) counts, at each visit in the first 6 months of FEDR Tx. Data were collected from February to March 2021. Mean spleen size, symptom count, Hb, and platelet and WBC counts at FEDR initiation vs at 3 and 6 months post-FEDR were compared via paired 2-sided t-test. Percentage reduction in spleen size and proportion of transfusion-dependent patients between FEDR initiation and 3 and 6 months post-FEDR were compared via 1-sided chi-square test. Only patients assessed at FEDR initiation (with palpable spleen or complete blood count available) and with a corresponding assessment at 3 or 6 months were included in the comparative analysis. Results: Among 150 eligible patients, the mean age at FEDR initiation was 68 years (range, 36–85). Median duration of RUX Tx prior to FEDR was 7.6 months (range, 0.7–65.5). At FEDR initiation, MF risk was categorized as International Prognostic Scoring System (IPSS)/Dynamic IPSS HR in 43% of patients, Int-2 in 37%, Int-1 in 9%, and unknown in 10%. A total of 74% of patients started FEDR at the recommended dosage of 400 mg daily. Median duration of post-FEDR follow-up was 5.1 months (IQR, 3.0–17.3) for patients initiated at FEDR 400 mg daily and 4.4 months (IQR, 3.0–14.3) for those initiating at <400 mg daily. At data cutoff, 55% of patients were still on FEDR. The primary reason for FEDR discontinuation was disease progression (43%). Mean duration of FEDR Tx was 4.7 months. Of 67 patients who discontinued FEDR, 44 were deceased at data cutoff. At FEDR initiation, 88% of patients had palpable spleen; mean spleen size was 16.0 cm (standard deviation [SD] 5.8) above the costal margin, which decreased to 13.2 cm (SD 7.9) at 3 months (P=0.0001) and 7.2 cm (SD 7.4) at 6 months (P=0.012). Mean number of MF-related symptoms declined significantly at 3 and 6 months; mean platelet count increased significantly at 6 months, from 160×109/L to 186×109/L (Table). Overall, 65.2% of patients experienced spleen size reduction, 18.8% had no change, and 16.0% had an increase. Mean best percentage change in spleen size was −29.2% (median −9.8%); complete resolution of palpable spleen occurred in 21% of patients. Image:Summary/Conclusion: This study illustrates the real-world effectiveness of FEDR after RUX failure in patients with Int- or HR MF. FEDR provided significant reductions in spleen size and reported number of MF-related symptoms after 3 months of Tx, including complete spleen responses. Greater benefits were observed with longer Tx duration.